Sputtering cathode and device and method for coating a substrate with several layers

ABSTRACT

The invention relates to a sputtering cathode ( 1 ) for coating a substrate ( 6 ), which comprises a device ( 5 ) for generating an external magnetic field with substantially parallel magnetic field lines ( 8 ) substantially in the plane of the substrate. The invention further relates to a device and a method for coating a substrate with several layers, whereby several sputtering cathodes are disposed in a circle with their target effective areas pointing radially outward.

The invention relates to a sputtering cathode for coating a substrate,in particular with magnetic and/or magnetizable materials. The inventionfurther relates to a device and a method for coating a substrate bymeans of cathode sputtering, in particular with magnetic materials.

DE-A-196 43 841 discloses a device for coating substrates, in particularwith magnetizable materials. Said device consists of a disk-shaped,rotatably supported substrate holder for receiving at least onesubstrate which, on its side facing away from the substrate and alongits periphery, is provided with a concentric dark space shield, a meansfor generating an outer field being parallel to the substrate plane, aswell as at least one cathode under which the substrate holder rotatesduring the coating process. The outer field of said device is generatedby an electromagnet having a yoke, wherein the lower yoke part with theexcitation coil is arranged in the dark space shield, and its elongatedpole shoes are arranged in an electrically separated manner in thesubstrate carrier close to the substrate. Inserted in the substrateholder, the substrate is rotated under the cathode and coated with thetarget material during dynamic operation of said device.

DE-A-41 35 939 discloses a rotationally symmetrical sputtering cathodewhich can also be configured as an elongated or long cathode. When saidsputtering cathode is configured as a long cathode, the substrate iscoated when moving it relative to the cathode.

Further prior art documents are WO 97/03220 A, EP 1 067 577 A, U.S. Pat.No. 4,601,806 A, U.S. Pat. No. 5,630,916 A, U.S. Pat. No. 6,217,272 B1,JP-05-171432 A and JP-01-004472 A.

The so-called MRAM (magnetic random access memory) is more and more usedin memory or storage technology as a non-volatile memory or storage. Inthese storage devices, the information to be stored is stored in themagnetization direction of a particle of a magnetic coating. There aretwo alternative methods of reading out the information, namely theso-called TMR (tunnel magneto resistance) effect and the so-called GMR(giant magneto resistance) effect.

For this kind of storage it is necessary to provide extremely thinlayers (on the order of few Å) which are extremely uniformly applied toa substrate. The storage capacity of this extremely thin layer isachieved by magnetizing the layer on the substrate. The easymagnetization axis of the magnetic material, e.g. a ferromagneticmaterial, is aligned in one direction over the entire area of thesubstrate. Deviations ranging at most between +/−2° are allowable whenaligning the easy magnetization axis.

Moreover, it is necessary for such magnetic storages to apply up to tenor more layers on one another.

By means of the sputtering cathodes known so far, it is not possible toproduce such extremely thin layers with the necessary accuracy asregards the alignment of the easy magnetization direction. The use ofrotationally symmetrical sputtering cathodes is, e.g., disadvantageousin that the rotationally symmetrical magnetic field in the sputteringcathode, which is necessary for the sputtering, disturbs the alignmentof the easy magnetization axis in the substrate layers in one direction.

It is a further disadvantage of rotationally symmetrical magnetronsputtering cathodes that, with the required layer thicknesses of few Å,the required extreme homogeneity and uniformity cannot be achieved.

It is a further problem related with the production of magnetizablelayers, in particular for MRAM, on a substrate that an extremely highvacuum is required in order to be able to apply the extremely thinlayers to the substrate as extremely uniformly as required.

It is the object of the invention to provide a sputtering cathode whichallows the easy magnetization axis of a magnetizable material to bealigned during the application of the material to a substrate.

Furthermore, it is intended to provide a device and a method for coatinga substrate with a plurality of layers of the same material or ofdifferent materials by means of cathode sputtering, and which issuitable for providing the plurality of thin layers of differentmaterials, which are necessary for magnetic storages, as extremelyuniformly as required.

In accordance with the invention, this object is achieved with thefeatures of the claims.

For applying magnetic materials to substrates, thereby achieving thenecessary alignment of the easy magnetization axis of the material, theinvention starts out from the basic idea of providing a sputteringcathode with a means for generating an external magnetic field, whereinthe magnetic field has essentially parallel magnetic field lines whichessentially lie in the plane of the substrate to be coated. Preferably,the strength of the external magnetic field can be varied in accordancewith the magnetic material used, so that when aligning the easymagnetization axis in the magnetic layer, the material used can be takeninto consideration.

More preferably, the sputtering cathode according to the invention is along cathode. The use of a long cathode is advantageous in that thestray fields caused by the magnet arrangement do not extend rotationallysymmetrical but overlap the essentially parallel magnetic field lines ofthe external magnetic field, so that these stray fields only play aminor role in the alignment of the magnetic particles. Moreover, the useof a long cathode leads to the advantage that the substrate to be coatedcan be easily moved under the target in its plane and perpendicular tothe longitudinal direction of the long cathode. This differencevis-à-vis the prior art (in which the magnetic field is moved togetherwith the substrate), i.e. the stationary external magnetic field of theinvention, leads to the specific advantage that upon a relative movementof the substrate under the target and through the external magneticfield, on the one hand, an easy and exact alignment of the easymagnetization axis can be achieved and, on the other hand, the desiredsmall layer thickness of the material to be applied can be adjustedeasily independent of the power of the sputtering cathode. With thiskind of coating, the speed of the substrate determines the thickness ofthe layer to be applied.

In the preferred embodiment, in which the sputtering cathode is a longcathode, the external magnetic field generation means extends along thelengthwise direction or longitudinal direction of the target of the longcathode. This means that along the entire length of the target anexternal magnetic field can be aligned essentially perpendicular to thelongitudinal direction of the target and essentially in the plane of thesubstrate, so that the easy magnetization axis of a material beingapplied to a substrate which is moved relative to the target can bealigned in the direction of the external magnetic field.

Since the substrate is necessarily arranged at a certain distance fromthe target during the coating process, a shield is preferably providedbetween the target and the substrate for shielding the area of thecathode which should not be coated.

Preferably, there is also a means for relatively moving the substratewith respect to the cathode during the cathode sputtering process. Morepreferably, this moving means provides for a translatory relativemovement of the substrate with respect to the cathode.

In the sputtering cathode according to the invention, the cathode basebody with the target arranged thereon is more preferably located in aprocess chamber, while the magnet arrangement allocated to the cathodebase body and the target is not provided in said process chamber but isseparated therefrom by means of a wall and located in the ambientatmosphere. This arrangement is particularly advantageous for providingthe ultrahigh vacuum which is necessary during the coating of substratesfor the provision of magnetic storages. By this preferred embodiment,i.e. separation between target and magnet arrangement, it is possible tomake the openings towards the process chamber much smaller because onlycooling fluid and current for the cathode have to be supplied to theprocess chamber. However, it is possible to combine them, so that onlythis combined supply has to be sealed in the preferred embodiment. Thus,much smaller sealing lengths are possible (so far, they wereapproximately one meter per target).

The device according to the invention for coating a substrate withseveral layers of different materials by means of cathode sputtering, inparticular with magnetic or magnetizable materials, is characterized inthat an arrangement is provided which consists of several sputteringcathodes, each having a cathode base body, each being provided with atarget made of the respective material and each having a magnetarrangement being located behind each target, wherein the severalsputtering cathodes are disposed on a circle with their respectivetarget effective areas pointing radially outward a nd the sputteringcathode arrangement is rotatable around the center of said circlerelative to the substrate. The substrate is essentially arranged in atangential plane of a circle surrounding the sputtering cathodearrangement.

This arrangement according to the invention in which several sputteringcathodes, which are necessary for the application of several differentlayers to the substrate, are arranged in the form of a circle or in theform of a drum makes it possible to achieve a very high uniformity andhomogeneity during the application of the several layers, because thesubstrate can be maintained in its plane during the various coatingsteps, while the different targets can be rotated into the respectivesputtering positions. The arrangement of the sputtering cathodes in theform of a target drum is further advantageous in that the entire coatingdevice is very compact. Such a target drum can be attached easily toconventional substrate supplying modules, for example in a lyingposition, i.e. with a horizontal longitudinal axis.

The sputtering cathodes are preferably long cathodes. The abovestatements are correspondingly applicable with respect to the relatedadvantages.

More preferably, the coating device according to the invention comprisesan external magnetic field generation means whose magnetic field linesextend essentially parallel and in the plane of the substrate. Thus, themagnetic particles are aligned with respect to their easy magnetizationaxis; the above statements are correspondingly applicable with respectto the related advantages.

The external magnetic field generation means is stationary relative tothe sputtering cathode arrangement, i.e. the sputtering cathodearrangement can be rotated relative to the magnetic field generationmeans. Depending on the target used, the latter is rotated in thecoating direction by rotating the sputtering cathode arrangement in thesputtering position relative to the substrate and is thus in the sphereof influence of the external magnetic field which acts on the layer thatis applied from the presently used target to the substrate.

Preferably, in the coating device according to the invention it is notnecessary that each sputtering cathode and/or each target has a separatemagnet arrangement for the generation of the magnetron magnetic field;rather, there is/are only one or two magnet arrangement(s) which canselectively be placed over the target to be used. This allows a furthercompaction of the coating device according to the invention, i.e. thetarget drum can have a relatively small diameter because in the interiorthere has to be space for one or optionally two magnetron magnetarrangement(s) only. For example, different magnet arrangements can thusbe provided or used for magnetic and non-magnetic target materials.

The method according to the invention for coating a substrate by meansof cathode sputtering, in particular by means of a sputtering cathodeaccording to the invention, is characterized in that during thesputtering process an external magnetic field is provided, wherein themagnetic field lines thereof extend essentially parallel and in theplane of the substrate.

In the method for coating a substrate with several layers, in particularwith magnetic materials, preferably a substrate is moved by atranslatory movement relative to a sputtering cathode essentially in theplane of the substrate, and thus a layer is applied to the substrate.This preferred movement of the substrate relative to the cathode canpreferably be repeated several times if this is necessary for achievinga required layer thickness. The sputtering cathode is subsequentlyreplaced with a different sputtering cathode having a target of adifferent material by rotating the drum, and the previous steps arerepeated.

The invention is particularly suitable for multilayer coatingsconsisting of many different materials even outside the field ofapplication of the MRAM technology.

In the following, the invention will be described in detail withreference to the drawings in which

FIG. 1 is a schematic sectional view of a sputtering cathode accordingto the invention in the form of a long cathode;

FIG. 2 is a schematic view of the alignment of the easy magnetizationaxis of a ferromagnetic material on a substrate;

FIG. 3 is a sectional view of the substrate coating device according tothe invention with long cathodes;

FIG. 4 is a sectional view of the preferred separation of the magnetarrangement and target according to the invention;

FIG. 5 is a schematic overview of a complete coating arrangementcomprising two coating devices according to the invention; and

FIG. 6 is a schematic oblique view of the moving means for thetranslatory movement of the substrate.

FIG. 1 is a cross-sectional view and shows the principle structure ofthe sputtering cathode 1 according to the invention with a long cathodewhose longitudinal axis is perpendicular to the drawing plane. Thesputtering cathode 1 according to this preferred embodiment has acathode base body 2 with a target 3 located thereon. Between target 3and cathode base body 2 there are cooling channels 9 for a coolingfluid. On the side of the cathode base body facing away from the target,a magnet arrangement 4 is provided whose magnetic field MF, i.e. themagnetron field, is shown below the target. The substrate 6 is spacedfrom the target 3. In the embodiment shown, the substrate 6 is locatedin a plane being essentially parallel to the target 3. Alternatively,the plane of the substrate can also be slightly inclined with respect tothe plane of the target 3.

Moreover, a means 5 for generating an external magnetic field in thearea of the substrate is provided. In FIG. 1, only the two pole shoes 5′of this means are shown; said pole shoes 5′ are electromagneticallyconnected with a coil arrangement (not shown). Said magnetic fieldgeneration means 5 generates an external magnetic field whose fieldlines 8 are shown in FIG. 1 between the pole shoes 5′. The magneticfield lines 8 of said external magnetic field or directional magneticfield essentially extend in the plane of the substrate 6 and thereinessentially parallel with each other, so that the desired parallelalignment of the easy magnetization axis MA is achieved in the substrate6.

Furthermore, a shield 7 between the target 3 and the substrate 6 shieldscomponents of the sputtering cathode that should not be coated againstthe sputtered target material; said shield 7 only forms a residual areaof the process chamber between target and substrate.

The desired alignment of the easy magnetization axis MA is achieved withthe sputtering cathode 1 according to the invention, namely both if thesubstrate 6 is moved during the coating process in its plane andessentially in the direction of the magnetic field lines 8 relative tothe target, and also if the substrate 6 rests under the target 3 duringthe coating process.

An optimum alignment of the easy magnetization axis is achieved inparticular if a long cathode is used because in this case the straymagnetic fields of the magnetron magnet arrangement 4 already overlapthe magnetic field 8 of the external magnetic field generation means 5.In the case of a rotationally symmetrical sputtering cathode or magnetarrangement 4, the stray magnetic field would not overlap the magneticfield of the external magnetic field generation means 5, which wouldpossibly lead to a deteriorated alignment of the easy magnetizationaxis. However, also such and other non-long-cathode arrangements formpart of the scope of the invention.

The alignment of the easy magnetization axis MA is schematically shownin FIG. 2. The alignment of the easy magnetization axis shown in FIG. 2,i.e. uniformly in one direction, is particularly important if thesubstrate to be coated is to be used as a magnetic storage, inparticular as an MRAM material.

FIG. 3 schematically shows a side view of the device 10 for coating asubstrate 6 with several layers of different materials by means ofcathode sputtering according to the invention. The upper part of theFigure shows the sputtering cathode arrangement 11 with the plurality ofsputtering cathodes 11-1, 11-2, . . . , 11-n. The sputtering cathodesare located on a circle with their target effective areas pointingradially outward, wherein the sputtering cathode arrangement 11 ortarget drum can be rotated around the center of said circle within adrum housing TG relative to the substrate. The substrate 6 can be movedwithin a housing G on a substrate holder 12 in the direction of arrow Prelative to the sputtering cathode arrangement, i.e. the target drum 11,horizontally and parallel with respect to the target surface of thetarget 3-i. The sputtering cathode 11-i, which is presently used for thecoating, is arranged together with the target 3-i at the lowermostposition in the target drum 11, i.e. above the coating position of thesubstrate 6. The drum housing TG and the housing G together form avacuum chamber which is evacuated via pumps (e.g. turbo molecular pumpsTP).

Optionally, depending on the desired layer thickness, one or more layersof the material to be sputtered from the target 3-i are applied to thesubstrate 6 by moving the substrate 6 once or several times horizontallybelow the target 3-i.

When sputtering with the target 3-i is finished, the target drum isrotated around its axis 15 until the sputtering cathode with the targetwith the different target material that is desired next has reached thesputtering position, i.e. the lowermost position of the target drum 11.Then the substrate 6 is optionally again once or several times movedbelow the target in order to apply a layer.

A shielding sheet 19 as well as the shield 7 serve the purpose ofshielding the environment against sputtered, unused target material.

If it is intended to also magnetize a layer applied to the substrate bymeans of the device according to the invention, a magnetic fieldgeneration means 5, as explained in connection with FIG. 1, is alsoprovided in accordance with the invention. If necessary, said means isactivated.

A multi-piece robot arm 13, which allows an extremely exact linearmovement of the substrate relative to the target drum 11, is providedfor moving the substrate holder 12 with the substrate 6. A transportingunit (not shown) transports the substrate 6 to the substrate holder 12at the robot arm 13 and again away therefrom.

Depending on the field of application, the target drum 11 comprisesseveral sputtering cathodes with targets. Eight or ten sputteringcathodes are preferred.

The targets 3-1 to 3-n of the different sputtering cathodes 11-1, 11-2,. . . , 11-n consist of different materials corresponding to the desiredcomposition of the layers to be applied to the substrate 6.

FIG. 4 shows the separation of target 3 and magnetron magnet arrangementaccording to the invention. The drum wall 17 of the target drum has onlya small opening for water and current supply. The target 3 is providedon a base plate, e.g. a copper plate 14, inside the process chamber.According to the invention, the magnetron magnet arrangement 4 (in FIG.4 only shown schematically) is separated from the process chamber andarranged outside the drum wall 17 (i.e. radially within the ring-shapeddrum 11). The distance between target 3 and magnetron magnet arrangement4 is preferably as small as possible.

FIG. 4 also shows insulating strips 16 which electrically insulate thecathode against the drum wall 17 and which also seal the evacuatedprocess chamber against the interior of the drum 18 which is undernormal pressure.

FIG. 5 shows a schematic top view of a complete coating assemblycomprising two coating devices 10 according to the invention beingcoupled to a supply module 30. The substrates to be coated areintroduced by the supply module 30 into the coating devices 10 and aresubsequently provided with the respective coatings in the coatingdevices. As shown in FIG. 5, the axes 15 of the target drums 11 arearranged perpendicular with respect to the movement directions (arrows Aand B) of the substrates from the supply module 30 into the coatingdevice 10. It has already been explained that in the coating device 10the substrate 6 is moved below the target 3-i which is located at thelowermost position. Depending on the desired coating structure on thesubstrate, the target drum 11 is subsequently rotated around the axis 15in such a manner that the following desired target is arranged above themovement path of the substrate 6 for coating the latter.

FIG. 5 furthermore shows two additional modules 20 by means of whichcoated or uncoated surfaces of the substrate can be further treated. Forexample, a surface can purposively be oxidized or optionally besmoothed.

FIG. 6 shows, similar to FIG. 3, a sectional view of a component of thecoating device according to the invention, i.e. the moving means(without housing G) for moving the substrate 6 below the target drum.FIG. 6 also shows the multi-piece robot arm which allows an exact linearmovement of the substrate 6 relative to the target.

1. A sputtering cathode (1) for coating a substrate (6), with magneticor magnetizable materials, comprising: a cathode base body (2); a target(3) arranged thereon; a magnet arrangement (4) provided behind thetarget (3) and intended for generating a magnetron field; a means (5)for generating a stationary external magnetic field having magneticfield lines (8) which extend essentially parallel with each other in thesame direction and essentially in the plane of the substrate (6); and ameans (13) for moving the substrate (6) during coating in its plane withrespect to the target (3) essentially in the direction of the magneticfield lines (8) of the external magnetic field.
 2. The cathode accordingto claim 1, wherein the cathode (1) is a long cathode.
 3. The cathodeaccording to claim 1, wherein the external magnetic field aligns an easymagnetization axis of a material being applied to the substrate (6). 4.The cathode according to claim 2, wherein the external magnetic fieldgeneration means (5) extends in a longitudinal direction of the target(3).
 5. The cathode according to claim 1, further comprising a shield(7) for shielding an area of the cathode (1) which should not be coatedbetween the target (3) and the substrate (6).
 6. The cathode accordingto claim 1, comprising a means for a particularly linear relativemovement of the substrate (6) with respect to the cathode (1) in thesubstrate plane during cathode sputtering.
 7. A sputtering cathode, inparticular according to claim 1, wherein the cathode base body (2) withthe target (3) provided thereon is arranged in a process chamber and themagnet arrangement (4) is separated therefrom by means of a wall andlocated in an ambient atmosphere.
 8. The sputtering cathode according toclaim 1, wherein strength of the external magnetic field is adjustable.9. A device (10) for coating a substrate (6) with several layers bymeans of cathode sputtering, with magnetic or magnetizable materials,comprising: a cylindrical cathode sputtering arrangement (11) comprisinga plurality of sputtering cathodes (11-1, 11-2, . . ., 11-n) each havinga cathode base body (2, 14), a target (3-1, 3-2, . . ., 3-n) arrangedthereon to provide a target effective area, and a magnet arrangement (4)provided behind the target (3) and intended for generating a magnetronfield; wherein the plurality of sputtering cathodes are located on acircle with their target effective areas pointing radially outward, andthe sputtering cathode arrangement (11) can be rotated around an axis(15) relative to the substrate (6) which is essentially arranged in thetangential plane of a circle enclosing the sputtering cathodearrangement (11); a means (5) for generating a stationary externalmagnetic field having magnetic field lines (8) which extend essentiallyparallel with each other in the same direction and essentially in aplane of the substrate (6); and a means (13) for moving the substrate(6) during coating in its plane with respect to target (3) essentiallyin the direction of the magnetic field lines (8) of the externalmagnetic field.
 10. The device according to claim 9, wherein thesputtering cathodes are long cathodes.
 11. The device according to claim9, wherein the external magnetic field aligns an easy magnetization axisof a material being applied to the substrate (6).
 12. The deviceaccording to claim 10, wherein the magnetic field generation means (5)extends in the longitudinal direction of the targets (3).
 13. The deviceaccording to claim 9, further comprising a means for a particularlytranslatory relative movement of the substrate (6) in the substrateplane and with respect to the sputtering cathode arrangement (11) duringcathode sputtering.
 14. The device according to claim 9, wherein thecathode base bodies (2) with the targets (3) arranged thereon areprovided in a process chamber and the magnetron magnet arrangements (4)are separated therefrom by means of a wall (17) and located in anambient atmosphere.
 15. The device according to claim 9, wherein onlyone or two magnetron magnet arrangement(s) (4) is/are provided for thesputtering cathode arrangement, wherein the cathode base bodies (2) withthe targets (3) arranged thereon are movable relative to the magnetronmagnet arrangements (4).
 16. A method for coating a substrate (6) bymeans of cathode sputtering, by means of a sputtering cathode accordingto claim 1, wherein a stationary external magnetic field having magneticfield lines (8) extending essentially parallel with each other and inthe plane of the substrate (6) is provided during sputtering.
 17. Amethod for coating a substrate with several layers-with magnetic ormagnetizable materials, in particular by means of the device accordingto claim 9, comprising the steps: (a) applying a layer on the substrate(6) by means of a sputtering cathode, wherein during sputtering astationary external magnetic field having magnetic field lines (8)extending essentially parallel with each other in the same direction andin the plane of the substrate (6) is provided; (b) replacing thesputtering cathode with a different sputtering cathode; (c) optionally atranslatory movement of a substrate relative to a sputtering cathode (1)essentially in the plane of the substrate (6) and essentially in thedirection of the magnetic field lines (8) of the external magnetic fieldduring step (a); and (d) repeating steps (a) to (c).
 18. The methodaccording to claim 17, thereby using a sputtering cathode comprising: acathode base body (2); a target (3) arranged thereon; a magnetarrangement (4) provided behind the target (3) and intended forgenerating a magnetron field; and a means (5) for generating astationary external magnetic field having magnetic field lines (8) whichextend essentially parallel with each other in the same direction andessentially in the plane of the substrate (6), wherein during coating,the substrate (6) can be moved in its plane with respect to the target(3) essentially in the direction of the magnetic field lines (8) of theexternal magnetic field.
 19. The method according to claim 16, whereinmovement speed of the substrate (6) in the substrate plane is controlledduring the application of the layer by means of cathode sputtering,depending on the desired layer thickness.